COL4A4 and Alport syndrome: Renal damage is the most life-threatening symptom of X-linked Alport syndrome (XLAS), an inherited disease caused by X-linked COL4A5 gene mutations, which cause more than 80% of all Alport syndrome cases (the remaining cases are caused by COL4A3/COL4A4 gene mutations) (Kruegel et al. 2013).